Optical transmission apparatus

摘要

In an optical transmission apparatus including an external optical modulator for modulating an optical carrier from a light source with an electrical signal, bias voltage applied to the external optical modulator is accurately adapted to fluctuations in optimal bias voltage due to DC drift. A bias voltage control circuit controls bias voltage applied by a bias voltage applier to an external optical modulator so as to minimize an amount of second order distortion included in an optical signal from the external optical modulator and caused by non-linearity thereof.